1. Field of the Invention
The present invention relates to a method of testing a ceramic article utilizing X-ray CT (computed tomography).
2. Description of the Prior Art
Ceramic articles have various advantages such as light weight, high mechanical strength, high corrosion resistance at high temperatures, and the like. With recent improvements in the quality of ceramic articles and developments in manufacturing methods thereof, studies are being made in many fields on the feasibility of replacing metals with ceramics.
However, ceramics are generally more brittle than metals and have microdefects which may lead to fracturing or damage to the articles consisting of such ceramics. In view of this, a demand has arisen for a method of nondestructively checking ceramic articles for microdefects which subsequently cause damage.
A nondestructive method utilizing transmitted X-rays is conventionally used for testing a metal article, especially a welded portion of a cast metal. However, ceramic articles to be tested include not only those of simple shapes such as plate-like or cylindrical ceramic articles but also those of complex shapes such as one-piece-shaped articles, e.g., turbo-charger rotors. When a ceramic article having such a complex shape is irradiated with transmitted X-rays, the level of noise is increased due to the complex profile and the correct discrimination of defects is difficult.
In the field of clinical medicine, X-ray CT (computed tomography) is used to obtain a tomograph of a living organism. It seems plausible to use this X-ray technique for testing ceramic articles. However, in this case, a false image, called an "artifact", is included in a tomograph of an object, such as a ceramic article, which has a high contrast and a more complex shape than a living organism. This "artifact" interferes with defect detection in a ceramic article. The "artifact" is a false image which appears when reconstructing a tomograph of a ceramic article based on data representing X-rays transmitted therethrough, and can therefore lead to erroneous detection of a normal portion of the ceramic article as a defect or vice versa.